Apparatus for lubricating the compressor of a refrigerating installation

ABSTRACT

FOR LUBRICATING THE COMPRESSOR OF A REFRIGERATOR INSTALLATION OPERATING ON A COMPRESSION CYCLE, THE UPPER PART OF THE COMPRESSOR CASING IS CONNECTED TO THE SUCTION SIDE AT A POINT WHERE THE PRESSURE IS LOWER THAN THAT IN THE EVAPORATOR, A HEAT EXCHANGER IS CONNECTED TO THE EVAPORATOR AND TO SAID UPPER PART, AND OIL IS PUMPED THROUGH THE HEAT EXCHANGER TO COOL IT AND IS THEN CONVEYED TO THE BEARINGS.

1971 H. BAUMGARTNER' APPARATUS FOR LUBRICATING THE COMPRESSOR OF A REFRIGERATING INSTALLATION Filed Aug. 6, 1969 FIG.

United States Patent 3,563,051 APPARATUS FOR LUBRICATING THE COMPRES- SOR OF A REFRI GERATIN G INSTALLATION Henri Baumgartner, Bernex, Geneva, Switzerland, as-

signor to Thermomeccanica Italiana, La Spezia, Italy Filed Aug. 6, 1969, Ser. No. 847,844 Claims priority, application Switzerland, Aug. 13, 1968, 12,170/ 68 Int. Cl. F25b 43/02 US. Cl. 62-468 4 Claims ABSTRACT OF THE DISCLOSURE For lubricating the compressor of a refrigerator installation operating on a compression cycle, the upper part of the compressor casing is connected to the suction side at a point where the pressure is lower than that in the evaporator, a heat exchanger is connected to the evaporator and to said upper part, and oil is pumped through the heat exchanger to cool it and is then conveyed to the bearings.

This invention relates to apparatus for lubricating the compressor of a refrigerating installation.

The lubrication of refrigerating installation compressors presents certain problems resulting from the mixture of the refrigerating medium with the lubricating oil. Thus, for example, sudden pressure drops in the lubricant reservoir, which may occur in particular when starting up the compressor, cause the refrigerating medium in solution in the oil to evaporate thus giving rise to the formation of foam. It has therefore been necessary to take certain precautions, in particular to apply pre-heating by an electric heater, in order to prevent the lubricating oil from penetrating in the form of foam into the bearings and thus prejudicing their operation. This pre-heating, however, reduces the stability of the refrigerating medium. Moreover, it is necessary to provide an oil separator downstream of the compressor and periodically to remove the oil which accumulates in the evaporator. The heat engendered by friction in the bearings must in addition be continuously removed, for example by a water-cooled heat exchanger.

It has been observed that the presence of foam in the evaporator, due to the presence of a small quantity of oil in the refrigerating medium, enables the quantity of refrigerant necessary to fill the evaporator to be substantially reduced, without the transfer of heat being affected. Since large refrigerating installations and, in particular, those comprising an evaporator of the type having tubes immersed in the refrigerating medium, necessitate the use of considerable quantities of this medium and since the cost of the latter represents in many cases a considerable proportion of the total cost of the installation, it is therefore evident that any method of reducing the quantity of refrigerating medium necessary in the installation will have a considerable economic interest.

An object of the present invention is a lubricating apparatus for the compressor of a refrigerating installation which will obviate the disadvantages of the known apparatus while enabling the necessary quantity of refrigerant to be reduced. According to the invention, there is provided lubricating apparatus for the compressor of a refrigerating installation operating on a compression cycle, comprising a first conduit connecting the upper part of the casing of the compressor to the suction side of the latter at a location where there exists a pressure lower than that which exists in the evaporator of the installation, a heat exchanger connected to the evaporator by a conduit for the flow of liquid refrigerating medium and to the upper part of the casing through a conduit for the discharge of refrigerating medium, a pump serving to aspirate oil from the casing and to return it through the exchanger in order to cool it, and a lubricating conduit for conveying the cooled oil to the bearings of the compressor.

The accompanying drawings represent, diagrammatically and by way of example, two forms of embodiment of the lubricating apparatus of the invention.

FIG. 1 is a diagram of a refrigerating installation comprising one form of lubricating apparatus; and

FIG. 2 is a diagram of a modified form.

Similar elements are indicated by the same reference numerals in the two figures of the drawings.

FIG. 1 shows a refrigerating installation comprising a compressor -1 connected through a suction conduit 2 to an evaporator 3 and through a return conduit 4 to a con denser 5. A condensate conduit 6 provided with a reducing valve 7 connects the condenser 5 to the evaporator 3. An electric motor M drives the compressor 1 having a drive shaft 8 mounted in bearings 9, 10 arranged in a casing 11 containing a bath 12 of lubricating oil. The evaporator 3 is, in the example shown, of the type having tubes 13 immersed in a bath 114 of boiling refrigerating medium, for example Freon of the R12 type. This refrigerating medium effects in this installation the wellknown cycle of refrigeration by compression, the medium which has evaporated in the evaporator 3 to a pressure P0 and a temperature T0 being aspirated through the compressor 1 and returned at a pressure Pc to the condenser 5 where it is condensed at a temperature Tc. The conduit 6 leads the condensed refrigerating medium to the evaporator 3 after passing through the reducing valve 7 which reduces its pressure to the pressure P0.

The lubricating apparatus further comprises a conduit 15 connecting the upper part of the casing 11 to a venturi tube 16 arranged in a suction conduit 2 in such a way that the velocity of the gaseous refrigerating medium is increased and consequently the static pressure is diminished in the venturi tube 16. The conduit 15 thus permits the gases located in the casing 11 to be extracted by the compressor 1 and the casing is thus maintained at a pressure P1 lower than the pressure P0 which exists in the evaporator 3. The lubricating device comprises, in addition, a heat exchanger 17 for cooling the lubricating oil which is being withdrawn from the bath 12 in the casing 11 by means of a conduit 18 provided with a pump .19. The cooled oil then passes from the exchanger 17, through the conduits 20, 21 and 22 to the bearings 9 and 10 in order to lubricate the latter and then flows into the oil bath 12. The cooling is effected in the exchanger 17 by means of liquid refrigerating medium withdrawn from the bath 14 of evaporator 13 via a conduit 23, the heated refrigerating medium then passing in a conduit 24 leading into the upper part of casing 11. The refrigerating medium thus flows from the evaporator 3 to the casing 11 due to the pressure difference PO-Pl. Moreover, because casing -11 is arranged above the evaporator -3, there is a convection effect due to the boiling of the refrigerating medium in the exchanger 17 and in the vertical conduit 24. The refrigerating medium thus evaporates while arriving at the upper part of casing 11 from where it is continually aspirated through conduit 15 by compressor 1.

The establishment, in the conduit 15, of the pressure difference P0P1 between the evaporator 3 and the casing 11 causes the circulation of a predetermined portion of the refrigerating medium through the heat exchanger 17, thereby enabling the lubricating oil to be maintained at an appropriate temperature by removal of the heat generated by friction in the bearings 9 and 10.

It is to be noted that the lubricating oil which is entrained with the refrigerating medium and led to the evaporator 3, is maintained at an almost constant proportion in the bath .14 of refrigerant due to the fact that the conduit 23 recycles the oil together with the liquid refrigerating medium towards casing 11.

Thus by means of the apparatus described above the bearings of the compressor can be effectively lubricated while eliminating the onerous precautions at present necessary to prevent migration of oil in the installation and to remove oil which has accumulated in the evaporator. The small quantity of oil contained in the bath 14 of refrigerant has no prejudicial effect on the transfer of heat in the evaporator 3; however, it causes foam to form in the latter so that the quantity of refrigerating medium necessary to form the bath 14 for immersing the cooling tubes 13 can be reduced. This presents an important economic advantage, in particular for large installations.

FIG. 2 represents a refrigerating installation similar to that described above and comprising a modified form of lubrication apparatus. The latter also comprises a heat exchanger 17 for cooling lubricant oil drawn off from bath 12 of casing .11 through a conduit 18 provided with a pump 19. A conduit 23 serves to withdraw liquid refrigerating medium from bath 14 and to lead it towards the exchanger 17 where it is heated and is then led through a conduit 24 in the upper part of casing 11. A conduit 15 and a venturi 16 serve, as in the case of FIG. 1, to maintain casing 11 at a pressure P1 less than the pressure P existing in the evaporator 3 and thus to aspirate gaseous refrigerating medium from casing 11.

In this second form of embodiment the cooled oil leaving the exchanger is led through a conduit 25 to a reservoir 26 to form in the latter a bath 27 of cold oil. This reservoir 26 communicates at its upper part, through a conduit 28 with the evaporator 3 and at a location where the refrigerant medium contained in the latter is in the gaseous state. The conduit 28 thus forms an overflow serving to return excess oil to the evaporator 3 where it mixes with the refrigerant medium of the bath 14. The oil serving to lubricate the bearings of the compressor is drawn off from the bath 27 through conduit 20 and is led to the bearings 9 and through the conduits 21 and 22 respectively.

Since the reservoir 26 is at the same pressure P0 as the evaporator 3, circulation of cold oil from the bath 27 towards the bearings 9, 10 takes place due to the pressure difference P0-P1. The pumping effect produced by the bearings 9 and 10 also assists this circulation. Thus, in FIG. 2, the pump 19 serves only to aspirate oil from casing 11 and to return it, through the exchanger 17 and conduit 25 to the reservoir 26.

The lubricating apparatus of the invention as described above, thus comprises a primary circuit for circulation of oil and a secondary circuit for circulation of refrigerant medium. This seconday circuit for cooling the oil, also serves to recover the oil located in the evaporator and to return it to the casing. For this purpose ,conduit 23 preferably communicates with the evaporator 3 at a point where the oil concentration is high, for example the lowest point of the bath of boiling refrigerant.

It has been found that it is advantageous to operate the installation in such a way that the bath of boiling refrigerant in the evaporator contains a small percentage of lubricant oil, for example 5% by weight in the case of Freon 12, in order to form foam in the bath and enable the tubes to be immersed with a relatively small quantity of refrigerant medium.

In the case of an installation of 500,000K calories/ hour, for example, the oil supply necessary for lubricating the bearings is of the order of 2 0 litres/minute, the oil becoming cooled from to 50%. Since the heat generated by friction in the casing is of the order of 3000K calories/hour, it is clear that the quantity of refrigerant medium withdrawn from the evaporator to effect the cooling of the oil is relatively small so that its effect on the efficiency of the installation is negligible.

I claim:

1. In a refrigerating installation operating on a compresion cycle and comprising a compressor, an evaporator and a condenser, apparatus for lubricating the compressor comprising a first conduit connecting the upper part of the casing of the compressor to the suction side of the latter at a location where there exists a pressure lower than that which exists in the evaporator of the installation, a heat exchanger connected to the evaporator by a conduit for the flow of liquid refrigerating medium and to the upper part of the casing through a conduit for the discharge of refrigerating medium, a pump serving to aspirate oil from the casing and to return it through the exchanger in order to cool it, and a lubricating conduit for conveying the cooled oil to the bearings of the compressor.

2. In a refrigerating installation according to claim 1, apparatus for lubricating the compressor further comprising a reservoir communicating at its upper part with the evaporator and at its lower part with the said lubricating conduit, said reservoir being fed with cooled lubricating oil from the heat exchanger.

3. In a refrigerating installation according to claim 1, apparatus for lubricating the compressor further comprising a venturi tube inserted into the suction conduit of the compessor and connected to the said conduit communicating with the upper part of the casing in such a way as to produce in the latter a pressure lower than that which exists in the evaporator.

4. In a refrigerating installation according to claim 2, apparatus for lubricating the compressor further comprising a venturi tube inserted into the suction conduit of the compessor and connected to the said conduit communicating with the upper part of the casing in such a way as to produce in the latter a pressure lower than that which exists in the evaporator.

References Cited UNITED STATES PATENTS 320,308 6/1885 Luckert 62-84 2,975,613 3/1961 Heidorn 62192 3,270,521 9/1966 Royner 62469 WILLIAM J. WYE, Primary Examiner US. Cl. X.R. 62-84 

